Well it's all fixed thanks (for now)
Told the wife that it's all down to me being a brilliant engineer.
Jack car up, took wheel off, nothing. Spun the hub may times, then noticed the faintest click at one point.
I sat there on the floor turning the hub listening to this, when I happened to accidentally lean on the inner dust shield ( I think that's what it is)
All of a sudden I get a grinding noise, so I pushed harder and spun the hub a few times and now it's gone !
Bear in mind this has been getting worse for about the last 1500 miles.
I can't see anything trapped or even where it could be.
Now to take this further, the ABS on my car is terrible, on the way to work there is a manhole that has always tripped the ABS (when wet) on any car I've driven.
When I cross it in the Defender it feels like brake failure, it trips the ABS as I cross it but the stopping power doesn't come back like you would expect it to.
So, is there a toothed ridge around the hub that the ABS picks up the wheel speed (that's hidden even with the wheel off)?
If so I wonder if there is muck in that that could be the cause of both the clicking and the brakes!!